1   How to write records to multiple streams partitioning by key

This tutorial shows how to build a multiple-partitioned writer, which writes records to streams partitioned by key.

1.1   Design a partitioner interface

In order to implement a multiple-partitioned writer, we need a Partitioner to partition the records into different streams based on their keys. The partitioner takes a KEY and its total partitions to compute a partition id for the given KEY.

public interface Partitioner<KEY> {
        int partition(KEY key, int totalPartitions);
}

1.2   Write records based on partition key

Once we have the Partitioner interface, it is easy to implement partitioned writer logic:

  • Partitioner takes a KEY and the total number of partitions, and compute the partition id for the key.
  • Use the partition id to choose the stream to write.
  • Use DistributedLogClient.write(stream, ...) to write the data to the chosen stream.
String[] streams = ...;
int pid = partitioner.partition(key, streams.length);
ByteBuffer value = ...;
client.write(streams[pid], value);

1.3   Run the tutorial

Run the example in the following steps:

1.3.1   Start the local bookkeeper cluster

You can use follow command to start the distributedlog stack locally. After the distributedlog cluster is started, you could access it using distributedlog uri distributedlog://127.0.0.1:7000/messaging/distributedlog.

// dlog local ${zk-port}
./distributedlog-core/bin/dlog local 7000

1.3.2   Start the write proxy

Start the write proxy, listening on port 8000.

// DistributedLogServerApp -p ${service-port} --shard-id ${shard-id} -sp ${stats-port} -u {distributedlog-uri} -mx -c ${conf-file}
./distributedlog-service/bin/dlog org.apache.distributedlog.service.DistributedLogServerApp -p 8000 --shard-id 1 -sp 8001 -u distributedlog://127.0.0.1:7000/messaging/distributedlog -mx -c ${distributedlog-repo}/distributedlog-service/conf/distributedlog_proxy.conf

1.3.3   Create the stream

Create the stream under the distributedlog uri.

// Create Stream `messaging-stream-{1,5}`
// dlog tool create -u ${distributedlog-uri} -r ${stream-prefix} -e ${stream-regex}
./distributedlog-core/bin/dlog tool create -u distributedlog://127.0.0.1:7000/messaging/distributedlog -r messaging-stream- -e 1-5

1.3.4   Tail the streams

Tailing the streams using MultiReader to wait for new records.

// Tailing Stream `messaging-stream-{1,5}`
// runner run org.apache.distributedlog.basic.MultiReader ${distributedlog-uri} ${stream}[, ${stream}]
./distributedlog-tutorials/distributedlog-basic/bin/runner run org.apache.distributedlog.basic.MultiReader distributedlog://127.0.0.1:7000/messaging/distributedlog messaging-stream-1,messaging-stream-2,messaging-stream-3,messaging-stream-4,messaging-stream-5

1.3.5   Write records

Run the example to write records to multiple stream in a console - the record should be in the form of KEY:VALUE.

// Write Records into Stream `messaging-stream-{1,5}`
// runner run org.apache.distributedlog.messaging.ConsoleProxyPartitionedMultiWriter ${distributedlog-uri} ${stream}[, ${stream}]
./distributedlog-tutorials/distributedlog-messaging/bin/runner run org.apache.distributedlog.messaging.ConsoleProxyPartitionedMultiWriter 'inet!127.0.0.1:8000' messaging-stream-1,messaging-stream-2,messaging-stream-3,messaging-stream-4,messaging-stream-5

1.3.6   Check the results

Example output from ConsoleProxyPartitionedMultiWriter and MultiReader.

// Output of `ConsoleProxyPartitionedMultiWriter`
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=utf8
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[inet] = com.twitter.finagle.InetResolver(com.twitter.finagle.InetResolver@6c4cbf96)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[fixedinet] = com.twitter.finagle.FixedInetResolver(com.twitter.finagle.FixedInetResolver@57052dc3)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[neg] = com.twitter.finagle.NegResolver$(com.twitter.finagle.NegResolver$@14ff89d7)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[nil] = com.twitter.finagle.NilResolver$(com.twitter.finagle.NilResolver$@14b28d06)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[fail] = com.twitter.finagle.FailResolver$(com.twitter.finagle.FailResolver$@56488f87)
May 08, 2016 1:22:35 PM com.twitter.finagle.Init$$anonfun$1 apply$mcV$sp
INFO: Finagle version media-platform-tools/release-20160330-1117-sgerstein-9-g2dcdd6c (rev=2dcdd6c866f9bd3599ed49568d651189735e8ad6) built at 20160330-160058
[dlog] > 1:value-1
[dlog] > 2:value-2
[dlog] > 3:value-3
[dlog] > 4:value-4
[dlog] > 5:value-5
[dlog] >


// Output of `MultiReader`
Opening log stream messaging-stream-1
Opening log stream messaging-stream-2
Opening log stream messaging-stream-3
Opening log stream messaging-stream-4
Opening log stream messaging-stream-5
Log stream messaging-stream-2 is empty.
Wait for records from messaging-stream-2 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-2
Log stream messaging-stream-1 is empty.
Wait for records from messaging-stream-1 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-1
Log stream messaging-stream-3 is empty.
Wait for records from messaging-stream-3 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-3
Log stream messaging-stream-4 is empty.
Wait for records from messaging-stream-4 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-4
Log stream messaging-stream-5 is empty.
Wait for records from messaging-stream-5 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-5
Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-2
"""
value-1
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-3
"""
value-2
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-4
"""
value-3
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-5
"""
value-4
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-1
"""
value-5
"""